Flow oscillations in the near-wake region of a two-dimensional circular cylinder are experimentally investigated at Mach 6 over the Reynolds number range $2.3\times {10}^5$ to $5\times {10}^5$. The oscillation frequency is obtained by spectral proper orthogonal decomposition of high-speed schlieren data. The Strouhal number based on the length of the near-wake shear layers is found to exhibit universal behavior. This corroborates experimental findings at Mach 4 from recent literature, and furthermore, the universal behavior is also seen to hold with respect to Mach number. Time-resolved pressure measurements at the flow separation points on the cylinder aft surface show that coherent oscillatory activity occurs with a phase difference of $\pi$ radians between the two statistically symmetric halves of the flow. This aspect of the flow dynamics at high speeds is in common with its low-speed counterpart, i.e., the canonical problem of the cylinder wake in an incompressible flow.

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• Compressible flows
• Compressible turbulence
• High-speed flow
• Shear flows
• Shock waves
• Wakes & jets